One of the measures of rock quality in terms of availability for flow:
{ \rm FZI } = \frac{\rm RQI}{\phi_z} |
where
\rm RQI | Rock Quality Index |
\phi_z | normalised porosity |
Unit = μm
It has much weaker dependence on effective porosity and shaliness and can be often considered constant within a given lithofacies which makes it a very efficient tool for lithofacies analysis
The constant FZI means that permeability strictly follows Cozeny-Karman permeability @model, although it's rarely met in practise.
The FZI depends on grains size distribution, shape and packing and can be modelled as follows:
(1) | {\rm FZI} = \frac{1}{\sqrt{F_S} \, S_{gV} \, \tau } |
where
S_{gV} = \Sigma_e/V_\phi | \Sigma_e | pore surface area | |
F_S | pore shape factor | V_\phi | pore volume |
\tau | pore channel tortuosity |
In some practical cases this can be further simplified to:
(2) | {\rm FZI} \approx 0.0037 \cdot \frac{d}{\tau } |
where
d | average grain size |
One of the proposed qualification of reservoir quality based on FZI is given by the Table 1.
Table1. One of the grade systems on reservoir quality based on FZI.
FZI Value | Reservoir Quality |
---|---|
FZI > 8.0 | Very Good |
3.5 < FZI ≤ 8.0 | Good |
1.0 < FZI ≤ 3.5 | Medium |
0.45 < FZI ≤ 1.0 | Poor |
FZI ≤ 0.45 | Very Poor |
See also
Petroleum Industry / Upstream / Subsurface E&P Disciplines / Petrophysics
[ Rock Quality Index (RQI) ] [ Absolute permeability @model ]